The present invention relates to a process for converting starches. More particularly, the invention relates to an acid conversion process whereby products having low viscosity and high levels of lower molecular weight compounds can be obtained.
Starches normally have good thickening properties because of their high molecular weight polymeric components. For applications that typically utilize a high starch (i.e., solids) content, such as adhesives, candies and food coatings, the common practice is to use starches that have been converted. The conversion process results in starch products that contain reduced molecular weight polymers and exhibit reduced viscosity.
The most common conversion methods used in the starch industry include acid hydrolysis, oxidation, pyroconversion, and enzyme conversion. Except for enzyme conversion, granular starch is used in the modification processes for ease of recovery. This recovery process generally involves a suspension of the final starch product in water, neutralizing the pH, then filtering out the starch product and washing the product with water. Such a process generally removes salts and charged particles, including the smaller molecular weight side products created during conversion.
The use of aqueous methods to convert starch which utilize the above described recovery method are well-known and described, for example, in publications such as xe2x80x9cStarch: Chemistry and Technologyxe2x80x9d, Second Edition, edited by Roy L. Whistler et al., Chapter X; Starch Derivatives: Production and Uses by M. W. Rutenberg et al., Academic Press, Inc. 1984.
There is a continuing need for an alternative conversion process that provides starches having lower viscosity and high levels of lower molecular weight compounds not heretofore observed in the art.
The present invention relates to a process for converting starches. More particularly, the invention relates to an acid conversion process whereby products having low viscosity and high levels of lower molecular weight compounds can be obtained.
The process of the invention comprises mixing a base starch with acid, drying the mixture to a substantially anhydrous state and heating the dried mixture for a sufficient time to produce a converted starch having a funnel flow viscosity of from about 5 to about 50 seconds.
The dry converted starches prepared via the foregoing process have a higher level of low molecular weight compounds than corresponding dry converted starches prepared via conventional aqueous acid conversion processes. The converted starches of the present invention demonstrate unique properties and, accordingly are useful in a number of products including adhesives, encapsulation matrices, confectioneries and paper surface sizing products.
The present invention relates to a process for converting starches with acid to give products having low viscosity and high levels of lower molecular weight compounds.
All starches and flours (hereinafter xe2x80x9cstarchxe2x80x9d) may be suitable for use as the base starch herein and may be derived from any native source. A native starch as used herein, is one as it is found in nature. Also suitable are starches derived from a plant obtained by standard breeding techniques including crossbreeding, translocation, inversion, transformation or any other method of gene or chromosome engineering to include variations thereof. In addition, starches derived from a plant grown from artificial mutations and variations of the above generic composition which may be produced by known standard methods of mutation breeding are also suitable for use as the base starch herein.
Typical sources for the base starches are cereals, tubers, roots, legumes and fruits. The native source can be corn, pea, potato, sweet potato, banana, barley, wheat, rice, sago, amaranth, tapioca, arrowroot, canna, sorghum, and waxy or high amylose varieties thereof. As used herein, the term xe2x80x9cwaxyxe2x80x9d is intended to include a starch or flour containing at least about 95% by weight amylopectin and the term xe2x80x9chigh amylosexe2x80x9d is intended to include a starch or flour containing at least about 40% by weight amylose.
Chemically modified starches may also be used as the base starch. Such chemical modifications are intended to include, without limitation, crosslinked starches, acetylated and organically esterified starches, hydroxyethylated and hydroxypropylated starches, phosphorylated and inorganically esterified starches, cationic, anionic, nonionic, and zwitterionic starches, and succinate and substituted succinate derivatives of starch. Procedures for modifying starches are well-known and described, for example in Modified Starches: Properties and Uses, Ed. Wurzburg, CRC Press, Inc., Florida (1986).
Physically modified starches may also be used as the base starch, including, without limitation, thermally inhibited or pregelatinized starches. Procedures for preparing thermally inhibited starches are disclosed, for example, in U.S. Pat. No. 6,221,420, and references disclosed therein, the disclosure of which is incorporated by reference. Exemplary processes for preparing pregelatinized granular starches are disclosed in U.S. Pat Nos. 4,280,851, 4,465,702, 5,037,929, and 5,149,799, the disclosures of which are incorporated by reference.
Whereas starches acid converted via conventional processes have been produced by dispersing the granular starch in water and adding acid to the mixture, it has now been discovered that mixing a base starch with acid, drying the mixture to a substantially anhydrous state and heating the dried mixture for a sufficient time to produce a converted starch having a funnel flow viscosity of from about 5 to about 50 seconds produces a starch having unique properties.
By a substantially anhydrous state means the starch mixture is dried to a moisture content of less than about 1%.
Generally, a base starch having less than about 18% moisture, is placed into a reactor having a convective and conductive energy source. Such reactors include, without limitation, a fluidized bed, a thin layer thermal reactor or a pressurized mixer equipped with vacuum and a heated jacket. A fluidizing gas (e.g. air) is then introduced at a rate whereby the starch is suspended in the reactor bed. Anhydrous acid (e.g. hydrochloric acid) and a carrier gas (e.g. nitrogen), are injected directly into the fluidizing gas of the fluidized reactor to effect the mixture of the starch and acid.
The temperature of the bed is increased to a temperature in the range of between about 50 to about 135xc2x0 C. The increase in temperature may be accomplished by means well known in the art including, without limitation, an oil-heated jacket or via a heated air source, or combinations thereof. Depending on the degree of acidification and initial moisture content, the reaction is typically completed within about 3 minutes to about one hour. Where the process is continuous, the process typically takes from about 3 minutes to about 30 minutes. A batch process is typically completed in from about 30 minutes to about one hour. While the reaction is substantially complete in less than about one hour, longer periods of heating, e.g. up to about 6 to about 8 hours or more, may be used without substantial deterioration of the final converted product. After the process is complete, the reactor is cooled and the starch discharged and used without the need for further purification.
In contrast, a conventional aqueous acid conversion process typically requires from about 12 to about 20 hours, and relatively more acid to effect the conversion of the starch, as well as additional purification and processing in the form of neutralization, filtration and drying. Since the purification process washes out low molecular weight components, the converted starches of the present invention which do not require purification, demonstrate a greater level of low molecular weight components than the corresponding converted starches prepared via a conventional aqueous procedure.
By adjusting the moisture content, degree of acidity and reaction conditions, the efficient process of the present invention may be tailored to produce a converted starch containing differing levels of lower molecular weight components. Additionally, the anhydrous process of the present invention enables the production of highly converted starches in a highly controlled and reproducible manner having a composition that would not allow for recovery if reacted in the presence of water (i.e., traditional aqueous batch processing). For example, products having a higher degree of conversion, which cannot easily be recovered from water, can be accomplished by preparing the starch according to the process of the present invention.
The starch compositions produced via this process demonstrate unique performance in certain products. Adhesives and encapsulation matrixes, for example, often require the addition of low molecular weight oligosacccharides or sugars to be added to the formulation for optimum performance. The starch compositions of the present invention advantageously provide desirable products without the need for the addition of lower molecular weight components. Further, the starches of the present invention are useful in products requiring unique gels and textures, including, for example confectioneries and paper surface sizing applications.
The following methods and examples are presented to further illustrate and explain the present invention and should not be taken as limiting in any regard. All parts and percentages are given by weight and all temperatures in degrees Celsius (xc2x0 C.) unless otherwise noted.